by Oren Dorell, USA TODAY

by Oren Dorell, USA TODAY

Boko Haram, whose name means "Western education is sinful," is among the most vicious terrorist groups operating in North Africa, home to some of the worst Islamic extremists in the world.

Boko Haram is responsible for more than 4,000 deaths in 2014, according to the Nigeria Security Tracker at the Council on Foreign Relations.

The group was begun in 2002 by Mohammed Yusuf, a cleric whose aim is an Islamic state in Nigeria. He was killed in 2009. The group's current leader, Abubakar Shekau, surfaces sporadically in videotaped messages.

Shekau was born in Shekau village, which borders Niger. He attended Borno State College of Legal and Islamic Studies. He is also known as "Darul Tawheed," which translates to an expert in monotheism.

His age is unknown. The U.S. State Department offered a $7 million reward in 2012 for information leading to his arrest.

In a video released in 2012 after an attack in Kano that killed nearly 200 people, Shekau said, "I enjoy killing anyone that God commands me to kill, the way I enjoy killing chickens and rams."

Boko Haram opposes the education of girls and has kidnapped girls to use as cooks and sex slaves. It has killed hundreds of children.

The group seeks to replace Nigeria's government with a ultra-strict Islamic state.

Its home base is the Sambisa Forest, a game preserve in Nigeria's northeast eight times larger than Yellowstone, and it has several hundred to a few thousand fighters.